I suggest you do a forum search in this forum for a recent thread called "one step forwards, two steps back" - because that was made by me (yes I have given away my anon thread, zomg) and it described EXACTLY this situation.
Now I don't want to patronise you at all, but I am very slightly older, I've had a gap year and also a first year at uni since my a-levels. In the grand scheme of life that isn't much however with first relationships and such it can make a massive difference.
This extra couple of years I think has given me one major difference to you about this, and I can't stress enough just how similar our situations are! You will not love him forever, and he is not the only one for you. Believe me, I was with my first ever girlfriend for two years and after that ended, I was saying EXACTLY the same things as you. If anyone had said what I am saying now I would have thought "well then it was different for you, but for me we really are perfect for eachother." But trust me on this one, no matter how good it is, it is attainable with other people. It's hard to conceive but try to believe me on this one because maybe I'm not in your mind, but I have had the exact thought processes you're typing up here recently.
So anyway, what is my point you may ask? My point is that difference in my way of thinking now from how it was before has let me do the right thing here with my second girlfriend. She says she doesn't want a relationship. Now I love her to death, I cry everyday whenever I think about her and my heart feels empty and there's this dreadful sense of longing.
HOWEVER, I have felt it all before, and moved on. I saw her on Saturday and had sex with her, held her - it was just like old times. As my thread says she has done the whole "I don't know what I want, I still love you, but I want alone time, don't wait for me in case we dont end up together, but maybe we will still end up together" line with me. For a little while I then told myself we WOULD work out, and I would wait for her even for that slim chance it would work.
However about two days ago I had an apifiny (sp) - hence my latest reply on my thread. I just realised that I was merely prolonging the agony and it was not worth it. Yes I love her, and yes you love your ex. However they have made their decision. They have made it admirably and they are doing what is best for them even if it means making such a difficult decision. I can't imagine how hard it must be to break up with someone you love. I applaud both your ex and mine for it.
In return for this we need to do the same. Say yes we had good times, and yes we still love them. But to wait around for something which may never last is unfair on us. Just move on, try to stay friends but get some space for at least a couple of weeks to reduce your feelings for eachother because they will blind you from what is the best thing for you both.
Above all else - don't give up. You're young, I'm young. We both have a lot to learn and new people and experiences along the way. I do wish things had worked out better and my ex wanted to stay with me. But in a way I also feel slightly happy this way. Do you expect to growold with whomever you meet when you're at sixth form, REALLY? It's so unlikely.
Hope this helped and once again I am really sorry if this has a patronising tone. I just relate to your experience so strongly I feltthe need to have a big old ramble about it!